The present invention relates to drivers and devices for delivering limited or regulated amounts of torque upon an object and, more particularly, to drivers that are capable of limiting the amount of torque delivered at varying settings.
Screwdrivers, wrenches and the like have been developed to allow for varying degrees of torque to be delivered upon an object. These devices allow for different tensions or torques to be built into a torque-limiting device. Generally, such drivers use springs in connection with a tensioning or biasing device to adjust or vary the amount of torque being delivered to an object. In certain devices and drivers, such as devices used in the medical field, these devices must be able to exert a large amount of force, while retaining a high level of precision. The large amount of force delivered by these devices tends to put a large amount of stress on the springs, which diminishes the strength of the spring, thereby reducing the precision of the spring.
Likewise, drivers and the like may be required to deliver differing amounts of torque at different times. That is, the same driver may be required to deliver a first amount of torque for a first procedure or step and a second amount of torque for a second amount of torque for a second procedure or step. These different steps still require precision. It is essential that one may be able to change from one setting to another accurately without losing precision. That is, the biasing means used in the devices should remain accurate even after several adjustments between varying tension settings. Previous designs that use springs, as discussed above, tend to wear after some use, thereby reducing the accuracy of the device.
Generally, prior art drivers use balls or ball bearings placed between to clutch plates or between a cam plate and a drive plate that work together with the springs to assist in the adjustment of the drivers. As the plates rotate relative to one another, the bearings slide within a grooved slot formed by the two plates, with the slot having varying depths. As torque is increased with the driver, the ball bearings will slide along the surface of the groove. When the torque becomes too much, the bearings will be forced into an area that prevents the two plates from working together with one another, thus preventing any further torque to be delivered to the driven object.
While able to limit the amount of torque being delivered, the drivers can take a lot of abuse, especially on the bearings themselves. Especially with medical applications, the amount of torque needed to be delivered can be several hundreds of pounds of pressure. When these devices trigger a torque cut-off or maximum torque level, the two plates will sandwich the bearings, exerting a large amount of pressure on the bearings. This smashing action of the bearings can cause damage to the bearings, which results in the effectiveness of the driver being diminished. This is not desirous for equipment requiring a high-level of precision, especially when the equipment can be rather expensive.
Thus, it would be advantageous to design a wrench or driver that could deliver differing amounts of torque at a high level of precision, which also delivers such precise torque levels consistently over many successive procedures.
Likewise it would be advantageous to develop a driver that could be adjusted between various torque levels, without losing any accuracy or precision after several uses or adjustments.